Filament type vegetation trimmers wherein a filament is rotated rapidly in a radial plane to provide a cutting element are becoming increasingly popular as an effective alternative to bladed trimmers. However, as the filaments used are generally composed of plastic materials, they are susceptible to wear and breakage and new cutting lengths must be supplied during operation.
In the class of filament trimmers wherein the filament is attached in individual precut lengths and in certain types of trimmers wherein a continuous supply of filament is carried by the slinger head, replacement of worn filament requires interruption of the trimming operation. Moreover, many trimmer configurations require that the trimmer be turned upside down for access to the filament support cite or to the stored supply. These methods of filament replacement are, therefore, cumbersome and inconvenient.
Other classes of filament trimmers in which a supply of filament is carried by the slinger head include what is commonly known as a "bump feed" trimmer wherein bumping the slinger head on the ground releases a predetermined length of filament for rotation. Although this class of trimmer does not require inversion of the trimmer for filament release or replacement, bumping the trimmer with sufficient force to actuate the release mechanism can require substantial effort which detracts from its overall convenience and ease of operation. Also, repeated bumping of the trimming apparatus can accelerate wear of the device and, particularly, of the bearings.
A still further class of trimmer includes those wherein filament is wound about a spool in a predetermined pattern such that when the filament has been worn to a relatively short length, the centrifugal force exerted on the filament during the trimming operation causes a section of the pattern of wound filament to unwind to expose a fresh cutting length. Although trimmers of this type do not necessitate cumbersome handling of the device for filament replacement, they have other disadvantages in that excessive lengths of filament can be released and in that the operator does not exercise direct control of the feeding process. Moreover, all types of trimmers wherein the filament supply is carried by the slinger head waste power in unproductive rotation of the entire filament supply.
To overcome the aforementioned difficulties and inconveniences inherent in the above described varieties of trimmers, a new variety of trimmer has recently been developed wherein a stationary filament supply is stored above the slinger head and fed out through a longitudinal feed passage for radial rotation by the slinger head. Although this practical arrangement is efficient and enables convenient access to filament supply, controlled, incremental release of fresh line is often difficult to achieve and the operator is often required to interrupt his work to feed out new filament manually, as needed.
Therefore, significant improvements in the convenience and efficiency of trimmer operations would be achieved by providing a filament feed mechanism for use in connection with trimmers of the aforementioned, new variety wherein the filament supply is carried above the slinger head, operable to release lengths of fresh filament incrementally without waste, without interruption of the trimming operation and without exertion or inconvenience to the operator.